The magnetic levitation molecular pump is taking advantage of a magnetic bearing adapted for suspending the rotor of the molecular pump in the air, so that there is no contact, friction and no lubrication is required during the rotation of the rotor of the magnetic levitation molecular pump with a high speed. Because of the aforesaid advantages of the magnetic levitation molecular pump, it is widely applied for obtaining vacuum environment with high vacuum and high cleanliness.
The structure of the magnetic levitation molecular pump is shown in FIG. 1, comprising a body of the magnetic levitation molecular pump, a rotor of the magnetic levitation molecular pump, a motor of the magnetic levitation molecular pump, a first radial magnetic bearing, a second radial magnetic bearing, a first axial magnetic bearing, a second axial magnetic bearing, a first radial protective bearing, a second radial protective bearing, an axial protective bearing, a first radial displacement sensor, a second radial displacement sensor, an axial displacement sensor and a controller of the magnetic levitation molecular pump, etc.
The rotor is stably suspended in a predetermined suspension center when the magnetic levitation molecular pump is working normally. The rotor may come into a state of subcritical vibrations when the rotor touches down to the protective bearing due to its instability caused by external disturbance. The subcritical vibration means a vibration whose frequency is less than a frequency that is synchronization with the rotating speed of the rotor. The subcritical vibration of the rotor mainly represents as a circular vortex motion, whose moving track is shown in FIG. 3, wherein, the circular vortex motion indicates a form of motion that the axial of the rotor moves back and forth around the center of a bearing. At this moment, the magnetic bearing comes into a nonlinear state, thus typical controller of the magnetic bearing cannot control the magnetic bearing for providing appropriate magnetic force so as to control the rotor effectively. The method for inhibiting subcritical vibrations of a magnetic levitation molecular pump rotor of prior art is quite roughly, and the typical controller of the magnetic bearing is unable to synchronize accurately with signals of subcritical vibrations of the rotor, thus cannot solve the problem of subcritical vibrations occurred in a circumstance of the rotor touch down, which means subcritical vibrations of the rotor cannot be effectively inhibited.